The confusion of chemical thermodynamics
Thread Content
I have learned thermodynamics, but I am still confused about what thermodynamics is. To put it simply, it is about studying the properties of PVT of fluids, but how can we show it in practical applications? For example, in the process of process calculation, the density of the fluid is calculated using different thermodynamic methods. The density calculated is very different: Q:Q. So how do we choose the appropriate thermodynamic method? How can we ensure that the calculated results are close to the actual results? How are the parameter constants in these thermodynamic equations determined? Can they only be determined through experiments?
Thermodynamics is very abstract. If you want to understand its essence, you cannot master it overnight. Only if you calm down and study it carefully can you possibly know its truth. Thermodynamics is discussed in all aspects of technology. Discussions of the effects of temperature, pressure, etc. on chemical equilibrium are also thermodynamic issues.
PVT properties are quite accurate for calculating physical properties. The main thing is to choose the correct model, but this depends on experience. Thermodynamic constants generally have calculation formulas.
My main experience is that it is mainly used to calculate physical property data. As long as you choose the right model, the accuracy is generally acceptable. I think thermodynamics is an applied subject, as long as you can look up models and calculate when you need to use it.
In fact, there is not much difference between thermodynamics and general mechanics. The object of general mechanics research is an object. Thermodynamics studies a group of objects. General mechanics is represented by a force F. Thermodynamics cannot express it, so it can only be expressed by a state function, that is, several parameters can be explained together. The status is different, and the objects of research are also different. This makes it easier to understand.
Chemical thermodynamics is one of the important subdisciplines of chemical engineering. Chemical engineering thermodynamics uses the principles of classical thermodynamics, combined with models that reflect system characteristics, to conduct thermodynamic analysis of chemical engineering processes. It studies the methods of obtaining physical property data, calculating and predicting thermodynamic properties, and calculating phase equilibrium in chemical engineering design and research. It also discusses the basic methods of thermodynamic analysis of chemical engineering processes, and calculation and prediction of thermodynamic properties.
Although there are many thermodynamic formulas, most of them have their own applicable conditions and assumptions. First, you need to choose the formula that best matches the system conditions you need to calculate. Secondly, because many formulas have many parameters, more general formulas will have parameter tables for different substances. You can choose those formulas with rich parameter tables for calculation. Generally speaking, as long as the calculation is not performed under high pressure and high temperature conditions, the error in the formula will not be too large.
The RK, SRK, and PR equations can be used to calculate the gas density, and the Rackeet equation can be used to calculate the liquid density.
The main contents of chemical thermodynamics include entropy balance calculation and analysis, heat balance calculation, material balance calculation, chemical reaction balance calculation, phase balance calculation, etc. It is an applied discipline based on physical property constants and thermodynamic calculations, and mainly studies equilibrium calculations. I have a simple understanding of chemical thermodynamics, please correct me if I am wrong!
Empirical formulas have an applicable scope, but sometimes for the same conditions, if the reference materials selected are different or the original authors are different, the experience will be different. Although the relative error of parameter calculation is not large in chemical engineering design, because the absolute flow rate is generally large, the absolute error will actually be larger, which can easily cause confusion for the calculator. In this regard, if the experts in the forum have time, they can recommend some commonly used manuals to everyone, so that you can get books as needed.
Practical applications require reference to literature. Thermodynamics contains too much content and is too difficult to master well.
Thermodynamics only studies the initial and final states of a system and does not consider intermediate processes. So all you need to know to calculate density is temperature and pressure.